diff --git a/spec/crisp/mal_specs/mal_spec_runner.cr b/spec/crisp/mal_specs/mal_spec_runner.cr
index a9e31fa..8b9198d 100644
--- a/spec/crisp/mal_specs/mal_spec_runner.cr
+++ b/spec/crisp/mal_specs/mal_spec_runner.cr
@@ -1,5 +1,5 @@
 class MalTestRunner
-  def initialize(@test_file)
+  def initialize(@test_file : String)
   end
 
   macro check_EOF